Mycobacterium tuberculosis (Mtb) causes tuberculosis (TB) in more than 8 million people worldwide and kills more than 1 million people annually. The Bacille Calmette-Gurin (BCG) vaccine is the most commonly used vaccine in the world, yet it does not effectively prevent Mtb infection or pulmonary TB in adults. New vaccines to supplement or replace BCG are urgently needed. The current standard of care for drug-sensitive TB consists of a 6-9-month drug treatment regimen. This long course of treatment is designed to prevent TB recurrence. Nonetheless, the incidence of recurrent TB is 2%-8%. A therapeutic vaccine administered as an adjunct to drug treatment could advance global efforts to improve and shorten TB treatment. IDRI has developed a novel vaccine candidate, ID93+GLA-SE, which has shown prophylactic and therapeutic efficacy in preclinical animal models of TB. Phase 1 studies yielded promising safety and immunogenicity results in uninfected adults in the US and in Mtb-infected and uninfected adults in South Africa. IDRI 203 is an ongoing Phase 2a trial funded by the Wellcome Trust that will evaluate ID93+GLA-SE for safety, dose selection, and immunogenicity in cured TB patients following a standard course of chemotherapy in South Africa. This is in preparation for a planned Phase 2b trial, IDRI 204, which will evaluate the selected dose for efficacy in the prevention of recurrence (PoR) of TB disease in cured TB patients. The immune responses that correlate with reduced risk of TB disease and/or protection against TB recurrence are not yet known. The IDRI 204 Phase 2b trial will be the first trial to evaluate vaccine efficacy for PoR, an important test of concept for TB vaccine strategy and provides a unique opportunity to identify immune correlates of risk for recurrent TB. However, conducting a broad range of immunological assays is cost-prohibitive. We therefore propose to evaluate and rank assays for their performance as potential biomarkers of recurrent TB in IDRI 203, a smaller, dose-finding study (n=60). Several innate and adaptive immunological responses are already being evaluated in IDRI 203. The evaluation of additional vaccine-induced immune responses would provide a broader characterization of ID93+GLA-SE immunogenicity in a post-treatment setting. We propose a longitudinal assessment of 23 cytokine and chemokine profiles from patient specimens using a multiplex assay. Humoral responses will also be characterized to determine titers of specific immunoglobulin subtypes. Additionally, we will develop a novel functional assay to measure the capacity of cellular specimens to inhibit mycobacterial growth and evaluate this assay as a potential in vitro correlate of in vivo vaccine efficacy. This project will result in important immunogenicity data to inform the next steps in clinical development of the ID93+GLA-SE vaccine and to further the post-treatment immunization concept as a strategy against TB. Identification of immune correlates of risk for recurrent TB would be a transformative event for the TB vaccine field, enabling hypotheses for surrogates of protection to be tested in future trial of candidate TB vaccines.